FORGE’d in the Early Universe: The Effect of Protostellar Outflows on Pop III Accretion

Feb 2, 2026·

Yasmine J. Meziani

Philip F. Hopkins

Michael Y. Grudić

Shivan Khullar

Claude-André Faucher-Giguère

Pratik J. Gandhi

Cite DOI arXiv ADS

Figure 1. Visualizations of the gas mass and gas kinetic energy surface densities in our cosmological simulation at redshift z ∼ 14. We highlight the dynamic range resolved in our simulation by zooming in from galaxy-wide scales on the left to the scales of the circumstellar disk on the right. In both density plots, the color increases from black to white (different properties use different color schemes) on a logarithmic scale, where each panel uses its own dynamic range. For the mass density plots (differentiated with a black through white color scheme) the median gas surface density (Σ_median) in the top left, top middle, and top right panels are 1.5 × 10⁻¹ M_☉ pc⁻², 1.7 × 10³ M_☉ pc⁻², and 2.3 × 10⁴ M_☉ pc⁻² respectively. For the bottom middle and bottom right panels, we see the bipolar outflows from protostellar jets (in bright red) extend out to ∼1 pc. The top right panel highlights a circumstellar disk extending out to ∼0.01 pc.

Abstract

We present a cosmological zoom-in radiation magneto-hydrodynamic (RMHD) simulation, using FORGE’d in FIRE, that follows the formation, growth, and evolution of a single metal-free Pop. III (proto)star at redshift z ∼ 14. The simulation captures a rotationally supported circumstellar disk and protostellar jets, both resolved down to <100 au scales. We find the star grows to ∼27 M_☉ over 31,000 years, with its final mass regulated by accretion and protostellar jets. Protostellar jets form because the magnetic mass-to-flux ratio lies within the regime that allows jet launching, and they are further enabled by a rotating circumstellar disk with sufficient gas–magnetic-field coupling, both present in this simulation. These jets regulate accretion onto the (proto)star and drive outflows that collide with infalling gas, slowing inflow at large radii due to the substantial momentum they carry. A circumstellar disk forms, extending out to ∼0.01 pc, which remains gravitationally stable (Q ≫ 1). The stability of the disk is maintained through both thermal support and turbulence. In this paper we focus on how jets play a critical role not only in shaping the final masses of Pop. III stars but also in directly influencing their surroundings by regulating accretion. These results will provide important insights into the initial mass function and feedback processes in the earliest star-forming regions of the Universe.

Type

Preprint

Publication

Submitted to Physical Review D